Madison police chief: Authorities investigating how 15-year-old school shooter obtained gun

USA TODAY - For more and to sign up click here Sarah Fortinsky Police in Madison, Wis., are investigating how the 15-year-old school shooter obtained a handgun. Police Chief Shon Barnes, in an interview Tuesday morning with CNN’s John Berman, said partners at the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are expediting a trace form “to determine the origin of that weapon, who purchased it, and how…